Purifree

Purifree is a fork from Purify that allows you to program in a point-free style, and adds a few new capabilities.

What is Purify?

Purify is a library for functional programming in TypeScript. Its purpose is to allow developers to use popular patterns and abstractions that are available in most functional languages. Learn more about Purify here

How to start?

Purifree is available as a package on Deno.land/x. Looking for the Node version? Here

import { map, chain } from "https://deno.land/x/purifree-ts@v1.2.3-rc1/mod.ts"

Purifree compatability

Purifree is 100% compatible with purify, and can be used interchangeably.

Point-free style

Point-free functions can be used with any ADTs (without needing module-specific imports), and can also be used together with the chainable (purify) API.

// pointfree: Maybe<string>
const pointfree = pipe(
  Just('name'),
  map((name) => name.toUpperCase()),
  filter((name) => name.length > 5),
  chain((name) => (Math.random() > 0.5 ? Just(name + ' lucky :)') : Nothing))
)
// matchTest: string
const matchTest = pipe(
  Right<number, string>(100),
  chain((num) => (num > 50 ? Right(num) : Left(`bad number: ${num}`))),
  caseOf({
    Right: (e) => 'Great number!' + e,
    Left: (e) => `OK number. | msg: (${e})`
  })
)

Kleisli

The function Kleisli can be used as an easy way to combine functions that return monads without using chain. If you need to use a long list of chains, you can use the Kleisli function to compose the functions instead of passing each one into chain. Instead of:

// getNameTest: ( name?: string ) => Maybe<string>
const getNameTest = (name?: string) => pipe(
  Maybe.of(name),
  chain((name?: string) => name ? Just(name) : Nothing),
  chain((name) => Just(name.toUpperCase())),
  chain((uppercasedName) => uppercasedName.length > 3 ? Just(uppercasedName) : Nothing)
)

Use:

// getNameTest: ( name?: string ) => Maybe<string>
const getNameTest = kleisli(
  (name?: string) => name ? Just(name) : Nothing,
  (name) => Just(name.toUpperCase()),
  (uppercasedName) => uppercasedName.length > 3 ? Just(uppercasedName) : Nothing
)
// result: Maybe<string>
const result = getNameTest('name')

Lifting

You can use the liftN family of functions to lift a function that takes normal values into a function that takes and returns elevated values. WARNING: If you try lifting a function that uses generics, it will probably loose its type due to typescript’s limitations.

// add takes normal values
const add = (num1: number, num2: number) => num1 + num2
// addL takes elevated values, and returns an elevated value
// addL: Lifted<(a: Ap<number>, b: Ap<number>) => Ap<number>> 
const addL = lift2(add)
// add5Option (b: Either<never, number>) => Either<never, number>
const add5Option = addL(Right(5))
// result: Either<never, number> = Right(15)
const result = add5Option(Right(10))

Codesandbox

You can try it out in the browser.